Transformer Volume Reduction: A New Analysis and Design of an SSSA Control-Based 20-kW High Power Density Wide Range Resonant Converter

Isolated dc/dc converters play a pivotal role in the realm of power electronics, particularly in the context of electric vehicle (EV) fast charging. These converters are responsible for delivering high-voltage direct current to EVs, sourced from a three-phase power factor correction converter, and exhibit compatibility with both low-voltage and high-voltage vehicle batteries. However, in many instances, the demand for constant power charging in various applications results in a significant portion of the transformer volume, thereby leading to a decrease in converter power density. This article presents a new analysis and design for a converter based on secondary-side semi-active (SSSA) control. This analysis provides theoretical support for transformer volume reduction and power density increase. It employs SSSA control to transfer stored energy from the transformer to the resonant network during boost operation, even when fs > fr, with the excitation inductance participating in resonance. Based on this analysis, the design of a 20-kW 650–850 V input to 300–900 V with 66.7A max output prototype is discussed. The objective is to achieve the highest feasible converter power density. The designed results confirm that the 2*PQ6535 (or 1*PQ6549) core can effectively serve the 20-kW transformer, resulting in an ultra-high power density of 14.36 kW/L (235W/in3).